A manifest changed by a sync (e.g. a page added on another device) could
be overwritten by the next autosave before disk_watch took it over, which
dropped that page from the list. save_manifest now notices that the file
is not the one the notebook in memory is based on and merges the two, with
that base as common ancestor; if there is nothing new to save here, the
other version simply stays.
Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>